2 (g.a.a.) Sedimentary Rock

If you have ever walked along a stream or beach you may have noticed tiny sand grains, mud, and pebbles. These are particles of sediment. Sediment is small, solid pieces of material that come from rocks or living things. In addition to particles of rock, sediment may include shells, and bones. Sedimentary rocks form when sediment is deposited by water and wind. Most sedimentary rocks are formed through a series of processes: erosion, deposition, compaction, and cementation.

Erosion: Destructive forces are constantly breaking up and wearing away all the rocks on Earth’s surface. These forces include heat and cold, rain, waves, and grinding ice. The forces of erosion form sediment. In erosion, running water, wind, or ice loosen and carry away fragments of rock.Deposition: Eventually, the moving water, wind, or ice slows and deposits the sediment in layers. If water is carrying the sediment, rock fragments and other materials sink to the bottom of a lake or ocean. Deposition is the process by which sediment settles out of the water or wind carrying it.Compaction: The process that presses sediments together is compaction. Thick layers of sediment build up gradually over millions of years. These heavy layers press down on the layers beneath them. The weight of new layers further compacts the sediments, squeezing them tightly together. The layers often remain visible in sedimentary rock.Cementation: While compaction is taking place, the minerals in the rock slowly dissolve in the water. Cementation is the process in which dissolved minerals crystallize and glue particles of sediment together. In cementation, dissolved minerals seep into the spaces between particles and then harden.